Blender operator that aligns transform to selected face

align_transform_to_selected_face.py

import bpy


class SimpleOperator(bpy.types.Operator):
    bl_idname = "mesh.align_transform_to_selected_face"
    bl_label = "Align Rotation to Selected Face"

    @classmethod
    def poll(cls, context):
        return context.active_object is not None and any(p.select for p in context.active_object.data.polygons)

    def execute(self, context):
        scene = context.scene
        
        scene.tool_settings.use_transform_data_origin = True
        prev = scene.transform_orientation_slots[0].type

        bpy.ops.transform.create_orientation(use=True)
        bpy.ops.object.editmode_toggle()
        transform_type = scene.transform_orientation_slots[0].type
        bpy.ops.transform.transform(mode='ALIGN', orient_type='Face', orient_matrix_type=transform_type)
        bpy.ops.transform.delete_orientation()
        
        scene.tool_settings.use_transform_data_origin = False
        scene.transform_orientation_slots[0].type = prev
        bpy.ops.object.editmode_toggle()
        
        return {'FINISHED'}


def menu_func(self, context):
    self.layout.operator(SimpleOperator.bl_idname, text=SimpleOperator.bl_label)


# Register and add to the "object" menu (required to also use F3 search for quick access).
def register():
    bpy.utils.register_class(SimpleOperator)
    bpy.types.VIEW3D_MT_object.append(menu_func)


def unregister():
    bpy.utils.unregister_class(SimpleOperator)
    bpy.types.VIEW3D_MT_object.remove(menu_func)


if __name__ == "__main__":
    register()